1. Field of the Invention
In at least one aspect, the present invention relates to treating metal surfaces with aqueous non-chromate acidic conversion coating compositions to increase the resistance to corrosion of the treated metal surface, either as thus treated or after subsequent overcoating with some conventional protective layer, such as organic-based protective layer.
2. Background Art
Conversion coating in general is a well known method of providing aluminum and its alloys (along with many other metals) with a corrosion resistant coating layer. Both traditional types of conversion coatings for aluminum, the chromate and phosphate types, are often environmentally objectionable, so that their use should be minimized for at least that reason. Non-chromate conversion coatings are relatively well known. For instance, conversion coating compositions and methods that do not require the use of chromium or phosphorus are taught in U.S. Pat. Nos. 5,356,490 and 5,281,282, both of which are assigned to the same assignee as this application.
In certain industries, and for certain applications, the end user of the conversion coated product dictates the level of corrosion protection that is sought from the conversion coating. For instance, OEMs have specific corrosion resistance tests for their aluminum alloy wheels. While certain conversion coatings have been suitable for imparting corrosion resistance to many types of surfaces, they have not been deemed acceptable for imparting corrosion resistance to other surfaces requiring a relatively high level of corrosion resistance, such aluminum alloy wheels.
Accordingly, is would be desirable to provide a conversion coating, a composition, and a process therefor that are at least as reliable for the surfaces requiring a relatively high level of corrosion resistance as that from conventional chromate conversion coating but minimizes, or most preferably entirely avoids, the use of chromium and phosphorus. Still other concurrent and/or alternative advantages will be apparent from the description below.
In at least one aspect of the invention an entirely or substantially chromium-free conversion coating composition and process for conversion coating metal surfaces is provided that provides adequate corrosion resistance in comparison with previously used chromate containing conversion coatings. In at least another aspect of the invention an article having a metal surface is provided wherein the metal surface is at least partially coated with an entirely or substantially chromium-free conversion coating that provides adequate corrosion resistance in comparison with previously used chromate containing conversion coatings.
In one embodiment, the present invention comprises an aqueous non-chromate acidic conversion coating composition that comprises, preferably consists essentially of, or more preferably consists of, water and:
(A) dissolved fluorometallate anions selected from the group consisting of TiF6xe2x88x922, ZrF6xe2x88x922, HfF6xe2x88x922, SiF6xe2x88x922, AlF6xe2x88x923, GeF6xe2x88x922, SnF6xe2x88x922, BF4xe2x88x92, and mixtures thereof; and
(B) a water-soluble polymer which is a Mannich adduct of poly(4-vinyl phenol) and N-methyl ethanolamine.
In at least another embodiment, the present invention comprises an aqueous non-chromate acidic conversion coating composition that comprises, preferably consists essentially of, or more preferably consists of, water and:
(A) dissolved fluorometallate anions selected from the group consisting of TiF6xe2x88x922, ZrF6xe2x88x922, HfF6xe2x88x922, SiF6xe2x88x922, AlF6xe2x88x923, GeF6xe2x88x922, SnF6xe2x88x922, BF4xe2x88x92, and mixtures thereof;
(B) a water-soluble polymer which is a Mannich adduct of poly(4-vinyl phenol) and N-methyl ethanolamine; and
(C) a water-soluble polymer which is a Mannich adduct of poly(4-vinyl phenol) and N-methyl glucamine.